Dissolution testing and analysis is required to be performed on sample substances manufactured by participants in various industries, such as the pharmaceutical industry, in order to assess therapeutic efficacy and/or other properties. The sample substances are often provided in the form of dosage units such as tablets, filled capsules, or transdermal patches. During a typical dissolution test procedure, the active components of the dosage units are released into solutions contained in specially designed test vessels under controlled conditions which may or may not be representative of the human digestive process, contact with the skin, or implantation within the body. Dissolution analysis by automated means has become popular for increasing throughput and improving accuracy, precision, reliability, and reproducibility. Automation also relieves the tedium of manually performing a variety of requisite procedures, including: handling and delivering dosage units such as capsules and tablets; monitoring dissolution system parameters; operating the spindle assemblies carrying the agitation paddles or baskets; recording, displaying and printing accumulated data and test results; controlling operations according to predetermined parameters such as time and temperature; and cleaning and filtering the vessels employed in such procedures.
One example of a known automated dissolution testing system is disclosed in U.S. Pat. No. 6,060,024 to Hutchins et al. The vessel rack holds a rectilinear array of six test vessels. The array consists of a front row of three equally-spaced, side-by-side test vessels, and likewise a back row of three equally-spaced, side-by-side test vessels. Separate, individual control heads are respectively mounted onto each test vessel. Each control head includes a housing or cover piece fitted onto a base plate. A number of operative components are mounted to or supported by each housing, including a liquid media sampling line, a retractable sampling probe with a servo motor and transmission components, a temperature detector, a waste aspirate line coupled to a drive assembly, a test vessel wash line, a media fill line, a pH adjustment and media replacement line, a carousel-type sample tablet dispenser coupled to a stepper motor, and an electrical interconnect board with an electrical cable. A paddle shaft extends into each vessel independently from the operative components comprising the control head for that vessel. All paddle shafts are driven by a common paddle drive assembly situated above the control heads.
The structural configuration of automated systems such as that disclosed in U.S. Pat. No. 6,060,024 does not facilitate access into the test vessels, and does not enable a high degree of visibility of the various components operating within the test vessels. In order to provide unobstructed access into the test vessels, the paddle drive assembly must be manipulated to remove each paddle shaft and each control head must be removed from its respective vessel. In addition, the control heads are quite large, so that the paddle drive assembly must be situated at a high elevation with respect to the test vessel. As a result, each paddle shaft is quite long and thus is prone to becoming misaligned in the test vessel or to wobble within the test vessel.